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Proceedings Paper

Flat-panel detector, CCD cameras, and electron-beam-tube-based video for use in portal imaging
Author(s): Hans Roehrig; Chuankun Tang; Chee-Way Cheng; William J. Dallas
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Paper Abstract

This paper provides a comparison of some imaging parameters of four portal imaging systems at 6 MV: a flat panel detector, two CCD cameras and an electron beam tube based video camera. Measurements were made of signal and noise and consequently of signal-to-noise per pixel as a function of the exposure. All systems have a linear response with respect to exposure, and with the exception of the electron beam tube based video camera, the noise is proportional to the square-root of the exposure, indicating photon-noise limitation. The flat-panel detector has a signal-to-noise ratio, which is higher than that observed with both CCD-Cameras or with the electron beam tube based video camera. This is expected because most portal imaging systems using optical coupling with a lens exhibit severe quantum-sinks. The measurements of signal-and noise were complemented by images of a Las Vegas-type aluminum contrast detail phantom, located at the ISO-Center. These images were generated at an exposure of 1 MU. The flat-panel detector permits detection of Aluminum holes of 1.2 mm diameter and 1.6 mm depth, indicating the best signal-to-noise ratio. The CCD-cameras rank second and third in signal-to- noise ratio, permitting detection of Aluminum-holes of 1.2 mm diameter and 2.2 mm depth (CCD_1) and of 1.2 mm diameter and 3.2 mm depth (CCD_2) respectively, while the electron beam tube based video camera permits detection of only a hole of 1.2 mm diameter and 4.6 mm depth. Rank Order Filtering was applied to the raw images from the CCD-based systems in order to remove the direct hits. These are camera responses to scattered x-ray photons which interact directly with the CCD of the CCD-Camera and generate 'Salt and Pepper type noise,' which interferes severely with attempts to determine accurate estimates of the image noise. The paper also presents data on the metal-phosphor's photon gain (the number of light-photons per interacting x-ray photon).

Paper Details

Date Published: 24 July 1998
PDF: 12 pages
Proc. SPIE 3336, Medical Imaging 1998: Physics of Medical Imaging, (24 July 1998); doi: 10.1117/12.317014
Show Author Affiliations
Hans Roehrig, Univ. of Arizona (United States)
Chuankun Tang, Univ. of Arizona (United States)
Chee-Way Cheng, Univ. of Arizona (United States)
William J. Dallas, Univ. of Arizona (United States)


Published in SPIE Proceedings Vol. 3336:
Medical Imaging 1998: Physics of Medical Imaging
James T. Dobbins; John M. Boone, Editor(s)

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